LOS ANGELES – Firefighters waged a desperate war on flames racing toward the Los Angeles city limits yesterday as Gov. Gray Davis declared the Southern California wildfires the most costly disaster in state history.

Brush fires have scorched an 815-square-mile swath of the Golden State from Ventura County, just northwest of L.A., to the Mexican border, killing at least 17 people, burning down 1,000 buildings and displacing 10,000 people from their homes as of yesterday.

Davis, putting the cash estimate on the devastation, said the firestorm will cost Californians $2 billion.

“It’s likely to be the most expensive disaster the state has ever experienced,” said Davis, the lame-duck governor who is leaving office Nov. 17.

The governor toured an evacuation center in Moorpark, to the east of Simi Valley, where a terrifying canyon blaze threatened L.A.’s heavily populated San Fernando Valley.